The present invention relates to display devices, and in particular, to a display device of a plasma display panel (PDP) and a digital micro mirror device (DMD).
For the display devices of PDP and DMD, there is used a sub-field method employing a binary memory for displaying a motion picture having a halftone by temporally superimposing a plurality of weighted binary images. Although the description below is provided for PDP, the same thing can be said for DMD.
The sub-field method will be described with reference to FIGS. 1, 2 and 3.
As shown in FIG. 3, a PDP having ten pixels arranged laterally by four pixels arranged longitudinally is now considered. The brightness levels of R, G and B of each pixel are each represented in eight bits, allowing the representation of brightness to be achieved with a 256-step gradation. The following description is provided for a G signal unless special comment is given, and the same thing can be said for R and B.
In FIG. 3, a portion indicated by the reference letter A has a brightness signal level of 128. If this is represented in binary digits, then a level signal of (1000 0000) is applied to each pixel in the portion A. Likewise, a portion indicated by the reference letter B has the brightness of 127, and a signal level of (0111 1111) is applied to each pixel in the portion B. A portion indicated by the reference letter C has the brightness of 126, and a signal level of (0111 1110) is applied to each pixel in the portion C. A portion indicated by the reference letter D has the brightness of 125, and a signal level of (0111 1101) is applied to each pixel in the portion D. A portion indicated by the reference letter E has the brightness of 0, and a signal level of (0000 0000) is applied to each pixel in the portion E. Each sub-field is obtained by arranging the 8-bit signals of the pixels in the vertical direction in the respective positions of the pixels and slicing the signal every bit in the horizontal direction. That is, according to an image displaying method using the so-called sub-field method for dividing one field into a plurality of differently weighted binary images and displaying the resulting image by temporally superimposing these binary images, each binary image obtained through the division is referred to as a sub-field.
The signal of each pixel is expressed as eight bits, and therefore, eight sub-fields can be obtained as shown in FIG. 2. A sub-field SF1 is obtained by collecting the least significant bits of the 8-bit signals of the pixels and arranging them in a 10xc3x974 matrix form. A sub-field SF2 is obtained by collecting the second least significant bits and similarly arranging them in a matrix form. According to the above manner, sub-fields SF1, SF2, SF3, SF4, SF5, SF6, SF7 and SF8 are formed. Needless to say, the sub-field SF8 is obtained by collecting the most significant bits and similarly arranging them.
FIG. 4 shows the standard form of a PDP drive signal of one field. As shown in FIG. 4, the standard form of the PDP drive signal has the eight sub-fields SF1, SF2, SF3, SF4, SF5, SF6, SF7 and SF8. The sub-fields SF1 through SF8 are sequentially processed, and the total processing is executed in a period of one field.
The processing of each sub-field will be described with reference to FIG. 4. The processing of each sub-field is comprised of a setup period P1, a addressing period P2, a sustaining period P3 and an erasing period P4. In the setup period P1, a single pulse is applied to a sustaining electrode E0, while a single pulse is each applied also to scanning electrodes E1, E2, E3 and E4 (the reason why only four scanning electrodes are shown in FIG. 4 is that only four scanning lines are shown in the example of FIG. 3 and a number of, for example, 480 scanning lines actually exist). By this operation, set up discharging is executed.
In the addressing period P2, the scanning electrodes in the horizontal direction are successively scanned, and only the pixel in which a data pulse is applied to a data electrode E5 at the timing when a wrinting palse is applied to the scanning electrode is subjected to specified writing. For example, during the processing of the sub-field SF1, the pixel indicated by xe2x80x9c1xe2x80x9d is subjected to writing and the pixel indicated by xe2x80x9c0xe2x80x9d is not subjected to writing inside the sub-field SF1 shown in FIG. 2.
In the sustaining period P3, one or more sustaining pulse (drive pulse) corresponding to the weight value of each sub-field is outputted. The pixel that has undergone writing and is indicated by xe2x80x9c1xe2x80x9d is subjected to plasma discharging in response to each sustaining pulse, and the specified pixel brightness is obtained through one process of plasma discharging. The weight of the sub-field SF1 is xe2x80x9c1xe2x80x9d, and therefore, the brightness of level xe2x80x9c1xe2x80x9d can be obtained. The weight of the sub-field SF2 is xe2x80x9c2xe2x80x9d, and therefore, the brightness of level xe2x80x9c2xe2x80x9d can be obtained. That is, the addressing period P2 is a period during which the pixel for emitting light is selected, while the sustaining period P3 is a period during which light emission is executed by the number of times corresponding to the quantity of weighting.
In the erasing period P4, the remaining electric charges are entirely erased.
As shown in FIG. 4, the sub-fields SF1, SF2, SF3, SF4, SF5, SF6, SF7 and SF8 are weighted by 1, 2, 4, 8, 16, 32, 64 and 128, respectively. Therefore, with regard to each pixel, the brightness level can be adjusted in 256 steps ranging from 0 to 255.
In the portion B of FIG. 3, light emission is executed in the sub-fields SF1, SF2, SF3, SF4, SF5, SF6 and SF7, and no light emission is executed in the sub-field SF8. Accordingly, there can be obtained the brightness level of xe2x80x9c127xe2x80x9d (=1+2+4+8+16+32+64).
In the portion A of FIG. 3, light emission is executed in neither one of the sub-fields SF1, SF2, SF3, SF4, SF5, SF6 and SF7, and light emission is executed in the sub-field SF8. Accordingly, there can be obtained the brightness level of xe2x80x9c128xe2x80x9d.
With regard to the standard form of the PDP drive signal shown in FIG. 4, the PDP drive signal has a variety of modifications, and these modifications will be described below.
FIG. 5 shows a PDP drive signal in a twofold mode. It is to be noted that the PDP drive signal shown in FIG. 4 is in a onefold mode. In the onefold mode of FIG. 4, the number of sustaining pulses included in the sustaining periods P3 of the sub-fields SF1 through SF8, i.e., the weighting values is 1, 2, 4, 8, 16, 32, 64 and 128, respectively. By contrast, in the twofold mode of FIG. 5, the number of sustaining pulses included in the sustaining periods P3 of the sub-fields SF1 through SF8 becomes 2, 4, 8, 16, 32, 64, 128 and 256, respectively, which are doubled in every sub-field. With this arrangement, the PDP drive signal in the twofold mode can display the image with the doubled brightness in contrast to the PDP drive signal of the standard form in the onefold mode.
FIG. 6 shows a PDP drive signal in a threefold mode. Therefore, the number of sustaining pulses included in the sustaining periods P3 of the sub-fields SF1 through SF8 becomes 3, 6, 12, 24, 48, 96, 192 and 384, which are tripled in every sub-field.
As described above, there can be formed a PDP drive signal in a sixfold mode at maximum, also depending on a margin in one field. With this arrangement, the image can be displayed with the sixfold brightness.
It is herein defined that the modal multiple is generally represented as N-fold. This N can also be represented as a weighting multiple N.
FIG. 7A shows the PDP drive signal in the standard form, while FIG. 7B shows a modified PDP drive signal having sub-fields SF1 through SF9 including the one additional sub-field. Although the last sub-field SF8 is weighted by 128 sustaining pulses in the standard form, the last two sub-fields SF8 and SF9 are each weighted with 64 sustaining pulses according to the modification of FIG. 7B. For example, when representing the brightness of the level of 130, the brightness can be obtained by using both the sub-field SF2 (weight of 2) and the sub-field SF8 (weight of 128) in the standard form of FIG. 7A. By contrast, the brightness can be obtained by using the three of the sub-field SF2 (weight of 2), the sub-field SF8 (weight of 64) and the sub-field SF9 (weight of 64) in the modification of FIG. 7B. By thus increasing the number of sub-fields, the weight of the sub-field that is heavily weighted can be reduced without changing the total number of levels of gray scale. By thus reducing the weight, the image display can be made clearer, allowing, for example, the pseudo contour noise to be reduced.
The number of sub-fields is generally represented by Z. In the case of the standard form shown in FIG. 7A, the number Z of the sub-fields is eight, and one pixel is represented in eight bits. In the case of FIG. 7B, the number Z of sub-fields is nine, and one pixel is represented in nine bits. That is, in the case where the number of sub-fields is Z, one pixel is represented in Z bits.
As described above, according to the sub-field method, gray scale representation can be achieved at various levels of brightness by changing the number Z of sub-fields, the weighting multiple N and the quantity of weighting of each sub-field.
However, some of gray scale levels include a pattern in which a plurality of sub-fields that emit no light are continuously existing before the sub-field that should emit light. When providing a gray scale level including the above pattern, the previous sub-fields do not continuously emit light, and therefore, the discharge for writing in the next sub-field that should emit light tends to be temporally delayed. Therefore, it is sometimes the case where no discharge for writing is executed depending on pixels. The sub-field that has undergone no writing has no chance of discharging and emitting light even when a sustaining pulse is subsequently applied after the addressing period. This has consequently led to the disadvantage of the occurrence of pixels that emit no light in a dotted style depending on gray scale levels. The existence of the pixels that emit no light naturally becomes a defect of the displayed image.
In order to solve this problem, it can be considered to satisfactorily execute the writing by setting the pulse width for the discharge for writing wide even if a lag of the discharge for writing occurs. However, if the writing pulse width is expanded in all the sub-fields, then the addressing periods P2 of the sub-fields become long to disadvantageously reduce the number of sub-fields that can exist in one field.
Accordingly, the present invention has the object of providing a display device capable of stably executing discharge for writing without reducing the number of sub-fields in one field.
In order to achieve the above object, the display device of the present invention provides a display device that executes gradational light emission at each pixel every field by forming Z sub-fields of first to Z-th from a video signal in which brightness of each of pixels in one field is represented by Z bits in such a manner that a first sub-field in which zeros and ones obtained by collecting only the first bit of Z bits from the whole screen are arranged is constructed and a second sub-field in which zeros and ones are obtained by collecting only the second bit of Z bits from the whole screen are arranged is constructed, weighting each of the sub-fields and outputting a number of drive pulses N times the given weight or a drive pulse having a time width N times the given weight, the device comprising:
a means for setting a writing pulse width of an attentional light-emitting sub-field wider than a normal writing pulse width at all gray scale levels in the case where at least two continuous non-light-emitting sub-fields exist before the attentional light-emitting sub-field at at least one certain gray scale level among all the gray scale levels specified on the basis of the number Z of sub-fields and the weighting of the sub-fields.
The expanded pulse width of the writing pulse should preferably be about 20 to 80 percent wider, and in particular, about 60 percent wider than the pulse width of the normal writing pulse.
According to the display device of the present invention, the width of the writing pulse may be expanded for the sub-field of which the weight is not smaller than a specified number. In this case, the specified number may be three, five or ten.
The display device of the present invention further comprises:
a time information source that stores time information of the sub-fields within one field for a variety of fields in which at least one of the number Z of sub-fields, the weighting multiple N and the weighting of the sub-fields is different;
a means for selecting an appropriate sub-field time information from the time information source on the basis of at least one of the specified number Z of sub-fields, the specified weighting multiple N and the specified weighting of the sub-fields; and
a means for regulating positions of sub-fields arranged within one field according to the selected sub-field time information,
whereby the sustaining periods of the sub-fields are arranged approximately in same positions within one field between fields.